This invention relates to a method and machine for forming articles from a plastic material. The present invention is particularly adapted for taking waste plastic materials of various heterogeneous make-up, and processing these materials into products which have properties similar to wood.
One example of a prior process for working up waste plastic material is known by the name of the "Reverzer" process, introduced by the Japanese company Mitsubishi Petrochemical, and mentioned in U.S. Pat. No. 4,187,352. According to this process, sorted or unsorted thermoplastic waste material of, for example, polyethylene, polypropylene, polyvinylchloride or mixtures thereof, is comminuted, and the particulate material is subsequently stored in a storage space. The particulate material is dried to a certain extent, using the heat released during the comminution of the waste material. From the storage space, the particulate waste material is supplied to the "Reverzer" unit, which in essence is a melting unit, comprising a hopper in which the material is softened, and a mixer comprising a screw member, in which the material is also fluidized. The fluid material is then injected under very high pressure into a closed mold and thus molded. The molds are then transported to a cooling space, and cooled by being sprayed with water. The molds are then opened and the molded product is removed. The resulting products may have the form of tapered beams, frames, U-beams, etc., depending upon the mold being used. In this prior process, a very high pressure is built up in the mixing and fluidization stage of the apparatus used, under the influence of which, as stated, the fluid material is injected into a special pressure resistant mold.
Klobbie U.S. Pat. No. 4,187,352, discloses a method for working up thermoplastic plastic synthetic material into shaped particles in which specially adapted pressure resistant apparatus is unnecessary, but commercially available non-pressure resistant apparatus and dies or molds can be used.
The Klobbie patent discloses apparatus in which the synthetic material is subjected to a mixing operation in a housing comprising a screw member, and is fluidized, molded, cooled in the mold, and removed from the mold. The synthetic material is supplied to an extruder without a screen pack and without an extrusion nozzle. The mold into which it is extruded is open at both ends so that the fluid is not under pressure within the mold. Molding pressure is obtained by mixing with the particulate synthetic material a blowing agent, the threshhold temperature of which is exceeded at the temperature occurring in the extruder. The blowing agent causes gas to be propogated so as to increase the pressure within the mold, thereby causing the plastic material to assume the shape of the mold.
Therefore, a primary object of the present invention is the provision of an improved machine and method for reprocessing waste polymers to create a molded product under low pressure.
A further object of the present invention is the provision of a machine and process which utilizes low pressure so as to permit the use of an inexpensive mold, but at the same time using a pressure which is higher than that shown in the Klobbie reference referred to above.
A further object of the present invention is the provision of a machine for molding waste polymers which creates a molding pressure within the extruder by use of a nozzle and a screen pack.
A further object of the present invention is the provision of an improved machine for processing waste polymers wherein the polymers can be contaminated with various impurities.
A further object of the present invention is the provision of a machine for processing waste polymers which includes a closure device for closing off the ends of the molds during the molding process.
A further object of the present invention is the provision of a machine for molding waste polymers at a low pressure, but which provides sufficient molding pressure without the need of a blowing agent as shown in the Klobbie patent.
A further object of the present invention is the provision of a machine which includes an automatic fill sensing device which senses when the mold is full and causes it to be indexed away from the extruder.
A further object of the present invention is the provision of a machine for processing waste polymers which utilizes a heating band to cause the waste polymers to achieve a fluid state for extruding.
A further object of the present invention is the provision of an machine which is economical to manufacture, durable in use and efficient in operation.